The present invention relates to optical transmitting equipment, an optical repeater, optical receiving equipment, and an optical fiber transmission system using an optical fiber amplifier and more particularly to supervision and a supervisory information transmission method for them.
The optical fiber amplifier has possibility of use in a future optical fiber transmission system. This system requires a means for supervising optical transmitting equipment (a data optical transmitter for converting data to data optical signals and an optical fiber amplifier are included), an optical repeater (an optical fiber amplifier is included), optical receiving equipment (an optical fiber amplifier and a data optical receiver for regenerating data from data optical signals are included), and an optical transmission line for connecting the above units and for transmitting the obtained supervisory information to the optical line terminal. The conventional supervisory information transmission art is indicated, for example, in Japanese Patent Application Laid-Open No. 3-214936. The above conventional supervisory information transmission art uses one of the methods that (1) a data optical signal and a supervisory optical signal which is multiplexed with the above data optical signal are amplified simultaneously by an optical fiber amplifier in each optical repeater and (2) a pumping light source is divided into two parts and one of them is used as a supervisory optical signal.
When an optical fiber amplifier having output in the saturated state is assumed, according to the above prior art (1), the supervisory optical signal is also inputted to the optical fiber amplifier simultaneously, so that the gain reduces and the output power of the data optical signal lowers in comparison with the case that only a data optical signal is inputted to the optical fiber amplifier. According to the above prior art (2), since the pumping light is divided for the supervisory optical signal, the pumping light power reduces and the gain also reduces, so that the output power of the optical fiber amplifier also reduces. The built-in optical fiber amplifier of the optical repeater is often used in the output saturated state. This is because it is necessary to increase the output power of the data optical signal as high as possible. However, there is a problem imposed that the use of the above prior art reduces the output power.